The present application is based on and claims priority from Japanese Patent Application 2000-280491 filed Sep. 14, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a permanent magnet type vehicle AC generator to be mounted in a passenger car or a truck.
2. Description of the Related Art
In order to improve fuel consumption of a vehicle, it is important to reduce energy loss of a vehicle AC generator. A permanent magnet type AC generator that has a permanent magnet is suitable because it does not have a field coil that consumes electric power for supplying field current.
However, it is difficult to control the output voltage of such a permanent magnet type AC generator without energy loss. A thyristor switching circuit has been used to short-circuit output terminals of an armature winding of the permanent magnet type AC generator to control the output voltage. However, energy loss due to short-circuit of the armature winding is considerably large.
Therefore, a main object of the invention is to provide an improved permanent magnet type AC generator having a voltage regulating system.
According to a main feature of the invention, a permanent magnet type vehicle AC generator for charging a battery includes a rotor having a permanent magnet, a stator having an armature winding, a rectifier and a control unit for short-circuiting the armature winding in synchronism with the rotation of the rotor. When the armature winding is not connected to a battery, the armature winding is not controlled by the control to generate a no-load voltage that is lower than a terminal voltage of the battery. On the other hand, when the armature winding is connected to the battery, the control unit intermittently short-circuits the armature winding to generate a regular voltage that is higher enough to charge the battery.
The armature winding may be comprised of a star-connected three phase windings having three output terminal ends. In this case, the control unit connects the neutral point of the three phase windings and the three output terminal ends through the rectifier. The armature winding may be comprised of a plurality of conductor segments having a rectangular cross-section connected each other to provide an armature winding of a very low armature resistance. The control unit is preferably comprised of an intermittent switch unit and a timing control unit that synchronizes the switching operation of the intermittent switch unit with rotation of said rotor.